As a scheme of encoding stereo acoustic signals at a low bit rate, an intensity stereo scheme is known. The intensity stereo scheme adopts a method of generating the L channel signal (left channel signal) and the R channel signal (right channel signal) by multiplying a monaural signal by a scaling factor. This method is also called “amplitude panning.”
The most basic method of amplitude panning is to find the L channel signal and the R channel signal by multiplying a time-domain monaural signal by a gain factor for amplitude panning (i.e. panning gain factor) (e.g. see Non-Patent Literature 1). Also, there is another method of finding the L channel signal and the R channel signal by multiplying a monaural signal by a panning gain factor every frequency component (or every frequency group) in the frequency domain (e.g. see Non-Patent Literature 2 and Patent Literature 3).
If panning gain factors are used as parametric stereo coding parameters, it is possible to realize stereo signal scalable coding (monaural-to-stereo scalable coding) (e.g. see Patent Literature 1 and Patent Literature 2). Panning gain factors are explained as balance parameters in Patent Literature 1 and as ILD (level difference) in Patent Literature 2.
Also, monaural-to-stereo scalable coding using panning for monaural-to-stereo prediction and encoding the difference between a stereo signal and an input stereo signal obtained by panning, has been proposed (e.g. Patent Literature 3).